1. Field of the Invention
The present invention relates to a method of forming a hole in a glass substrate by using a pulsed laser, and a method of producing a glass substrate provided with a hole.
2. Description of the Related Art
A technique has been know, so far, that is for forming one or more through holes in a glass substrate by irradiating a laser beam, such as a CO2 laser, onto a glass substrate. Recently, in order to form a more finer through hole, it has been studied to perform through hole processing by using a pulsed laser, as the laser.
For example, it is described in Non-Patent Document 1 (Journal of the Japan Society for Precision Engineering, Vol. 64, No. 7, 1998, pages 1062-1066) that, during processing, a pigment that favorably absorbs a laser beam is applied to a surface of a glass substrate, so that energy density of a pulsed laser is decreased.
For a case where a pulsed laser is used, for example, a fine hole with a diameter that is approximately less than or equal to 30 μm can be formed in a glass substrate.
However, since peak power of a pulsed laser is greater than peak power of a laser, such as a continuous wave (CW) laser, a crack and/or a defect tends to occur in the glass substrate during a hole forming process and/or after forming a hole. In addition, when energy density of a pulsed laser is lowered so as to avoid occurrence of such a crack and/or a defect, processing time for forming a hole in the glass substrate becomes longer, or a hole may not be formed.
Note that, by the experiment by the inventors, it has been found that a crack and/or a defect may occur, even if the method described in Non-Patent Document 1 is used.
There is a need for a method with which a hole can be formed in a practical time by using a pulsed laser, without significantly generating cracks and/or defects in a glass substrate.